a. Field of the Invention
This invention relates to an improved method of producing carbonaceous or graphitic articles in fibrous form having high anisotropy be selecting a substance having particular chemical structure and properties as a carbon precursor. (The carbonaceous or graphitic fibers will hereinafter be called in general term "carbon fibers".)
B. Discussion of Prior Arts
There have been known several methods of producing carbon shaped articles, particularly carbon fibers, representative methods of which are as follows:
(1) A method, in which the fibers made of natural or synthetic high polymer materials such as polyacrylonitrile, polybenzimidasole, cellulose, etc. are baked.
(2) A method, in which pitch as a raw material is formed into a fibrous shape by melt-spinning, thereafter subjecting the fibers to infusibilization treatment and then to carbonization.
The abovementioned second method has been invented by one of the present inventors, and is suited for obtaining products of uniform quality and high strength, as taught in U.S. Pat. No. Re. 27,794 (Otani) and No. 3,629,379 (Otani).
The characteristic feature of producing the carbon fibers from pitch as taught in the abovementioned patents is such that natural or synthetic organic compounds are baked at a temperature of from 300.degree. to 500.degree. C (heat-treatment in an inert gas atmosphere) to obtain a pitch substance in a molten state, then the molten pitch substance is subjected to meltspinning, and the thus spun filaments are oxidized to infusibilize so that the individual filament may not be fused together by further heat-treatment, after which the infusibilized filaments are subjected to carbonization. In this case, the melt-spinning is carried out by using the raw material pitch of a particular class having a mean molecular weight of 400 and above. The thus spun filaments are then subjected to the infusibilization treatment and carbonization, followed by, if necessary, the graphitization treatment, thereby obtaining the carbonaceous or graphitic fibers.
However, no precise study has ever been made as to the molecular orientation of the carbonaceous or graphitic fibers obtained by the patented methods, and the relationship between the crystal growth and the physical properties or structure of the raw material pitch as well.
The present inventors have conducted further studies and experiments on the abovementioned problems, and have finally found out that carbonaceous or graphitic fibers having high modulus of elasticity and excellent crystal orientation, particularly high anisotropy, can be obtained by the use of carbon precursors with particularly orientable molecular class as the principal constituent.
The present invention is directed to a more limited definition of the pitch in its physical properties to suit the purpose of obtaining carbon fibers having the modulus of elasticity of 1,400 tons/cm.sup.2 and above, which is at the present moment made the object of practical use as the cabonaceous or graphitic fibers for reinforcement purpose.